[Python-ideas] bool(datetime.time(0, 0))

[M.-A. Lemburg]

Nick Coghlan wrote:
> On Tue, May 8, 2012 at 3:42 PM, Steven D'Aprano <steve at pearwood.info> wrote:
>> On Tue, May 08, 2012 at 01:57:13PM +1000, Nick Coghlan wrote:
>>> On Tue, May 8, 2012 at 12:57 PM, Ethan Furman <ethan at stoneleaf.us> wrote:
>>>> The behavior is broken.  Midnight is not False.
>>>
>>> Whereas I disagree - I see having zero hour be false as perfectly
>>> reasonable behaviour (not necessarily *useful*, but then having all
>>> time objects report as True in boolean context isn't particularly
>>> useful either).
>>
>> On the contrary, it can be very useful to have all objects of some
>> classes treated as true. For example, we can write:
>>
>> mo = re.search(a, b)
>> if mo:
>>    do_something_with(mo)
>>
>> without having to worry about the case where a valid MatchObject happens
>> to be false.
>>
>> Consider:
>>
>> t = get_job_start_time()  # returns a datetime.time object, or None
>> if t:
>>    do_something_with(t)
>>
>>
>> Oops, we have a bug. If the job happens to have started at exactly
>> midnight, it will wrongly be treated as false.
> 
> IMO, you've completely misdiagnosed the source of that bug. Never
> *ever* rely on boolean evaluation when testing against None. *Always*
> use the "is not None" trailer.

Fully agreed.

The above code is just plain wrong and often causes problems
in larger applications - besides, it's also slower in most
cases, esp. if determining the length of an object or
converting it to a numeric value is slow.

If you want to test for None return values, you need to use
"if is None" or "if is not None".

-- 
Marc-Andre Lemburg
eGenix.com

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